Project Summary/Abstract The proposed project is a new submission by a New and Early Stage Investigator for an R01 (Funding Opportunity Announcement PAR-16-260). The vast majority of alcohol use takes place in social settings, yet nearly all human experimental research has administered alcohol to individuals in isolation. This research setting dampens reports of alcohol stimulation, increased positive affect, and decreased negative affect, and it makes it impossible to measure many of the subjectively pleasant social effects of alcohol that confer increased risk for alcohol use disorder (AUD) (e.g., increased sociability, decreased social anxiety). Notably, to date, laboratory subjective responses to alcohol (SRA) in isolation have accounted for between just 4% and 6% of the variance in future AUD symptoms. The proposed study will be the first to examine the effects of alcohol in social groups across a number of domains hypothesized to mediate alcohol use, and to test whether these responses can better predict the development of AUD symptoms. Further, this study will be the first to examine intermediate real-world drinking experiences using ecological momentary assessment (EMA) methods in order to evaluate how lab-based SRA translate to risk processes outside of the laboratory. Three-hundred-eighty-four heavy drinkers (50% female; aged 21-25) will be assembled into 128 three- person groups. All members of each group will drink over 36-min a moderate dose of alcohol (males: 0.82 g/kg; females: 0.74 g/kg) or a placebo beverage; SRA and social reward (e.g., social bonding) will be assessed using a broad range of measures across multiple response systems (e.g., self-reports, observational measures of smiling and speech patterns). Drinking behavior, SRA, and acute alcohol- related problems will be assessed in daily life during three subsequent EMA bursts, and AUD symptoms will be assessed at baseline and at 12-month follow-up. We predict that participants drinking alcohol will experience more stimulation/positive affect, craving, and social reward (e.g., social bonding) and less sedation, negative affect, and social discomfort on the ascending limb of the blood alcohol curve, measured across multiple response systems, than those drinking placebo. Further, we predict that these lab-based SRA and social reward indices will be clinically meaningful?that is, we expect that they will prospectively predict SRA, heavier alcohol use, and more acute alcohol-related problems in daily life, and more AUD symptoms at 12-month follow-up. Finally, we predict that SRA in daily life will mediate the link between laboratory SRA and AUD symptoms. We will also test whether individuals at risk for AUD (e.g., due to personality, genetics) are especially sensitive to alcohol's effects in the lab and in daily life and whether this predicts heavier alcohol use and the development of more AUD symptoms over time. This work, by developing a laboratory social drinking paradigm that predicts real-world alcohol responses and AUD risk, can serve as the next generation model for identifying lab-based predictors for future AUD symptoms.